EYE 



233 



The muscles of the eyeball and of the third eyelid ai^e 8 in 

 number, of which 6 serve to move the eyeball. Four recti, viz. 

 superior, inferior, internus, and externus arise from the orbit in the 

 vicinity of the optic nerve ; the first three are innervated by the 



J?, inf. 



m.if. 



Left Eye or the Common Fowl froji Front and Behind. 

 O.if. Musculus obliquus inferior; H.if. R.int. E.s. R.e. M. rectus inferior, internus, superior, 

 and externus ; Q. M. quadratus ; P. M. pyramidalis. 



n. oculomotorius or 3rd cranial nerve, and the externus by the n. 

 abducens, or 6th cranial nerve. 



The m. obliquus superior arises from the ethmoidal margin of 

 the orbit, passes between the olfactory and the first branch of the 

 trigeminal nerve, is supplied by the n. trochlearis or 4th cranial 

 nerve, and is inserted upon the upper and inner side of the 

 eyeball. 



• The m. oblicjuus inferior arises below the optic nerve, and is 

 inserted laterally from the inferior 



P.U.Q 



R.exi. 



R.int. 



rectus ; it is supplied by the 3rd 

 cranial nerve. 



The nictitating membrane is 

 moved by two muscles, both of 

 which are innervated by the 6th 

 cranial nerve. The m. cpiadratus 

 is a trapezoid muscle, arising with 

 a broad base from the hinder sur- 

 face of the eyeball, and forming 

 with its narrow margin, which is 

 directed towards the optic nerve, 

 a pulley for the long tendon of 

 the m. pyramidalis. The latter 

 arises from the nasal or median 

 surface of the eyeball, passes into 

 a tendon, which runs above the „ . , ... „.,. , . 



, , , ., Bram); ciiia res, Ciliary nerves supplying the 



optic nerve through the pulley and internal muscles of the eye, e.g. Crampton's 



goes over on the anterior side of muscle ;— the swelling at the root of these 



the eye into the nictitating mem- nerves is the ciliary ganglion. 



Irane. The latter is a transparent, slightly whitish membrane, 

 which arises with a broad base from the upper outer margin of the 

 eye as a duplication of the conjunctiva. Contraction of the pyra- 



Vextral View of the Nerves of the 

 Left Eyeball of Rhea americana. 



V.i.i. First branch of uervus trigeminus : 

 VI, Nervus abducens, innervating the mus- 

 culus rectus externus, m. pyramidalis, and 

 m. quadratus ; R.s. R.inf. R.int. Obi. inf. 

 Branches of the nervus oculomotorius (see 



